Organic electroluminescence elements are being developed enthusiastically in order to use the elements in applications such as displays and lightings. An organic electroluminescence element is usually configured at least of a pair of electrodes and an organic luminescent layer interposed therebetween. The organic electroluminescence element emits light usually by the following mechanism. An electric field is applied between the electrodes and, as a result, electrons and holes are injected respectively from the cathode and the anode into the luminescent layer, where the electrons recombine with the holes to yield excitons, which cause the element to emit light.
However, since the charge injection into the luminescent layer necessitates a large amount of energy, a high voltage is necessary for causing the organic electroluminescence element to luminesce at a high luminance. In addition, the life of the element is short.
Under these circumstances, patent document 1 discloses a technique in which a plurality of electron transport layers are disposed between a luminescent layer and an electrode and the electron affinity of each layer is regulated so as to satisfy [(electron affinity of the luminescent layer)<(electron affinity of the electron transport layer which adjoins the luminescent layer)<(electron affinity of the electron transport layer which is the second layer from the luminescent layer)< . . . (electron affinity of the electron transport layer which is the n-th layer from the luminescent layer)], thereby enhancing charge injection and improve operation durability.